The present invention relates to a disc drive microactuator, and more particularly to a magnetic microactuator utilizing a magnetic circuit having simplified assembly, reduced field leakage, and improved passivation methods.
The density of concentric data tracks on magnetic discs continues to increase (that is, the size of data tracks and radial spacing between data tracks are decreasing), requiring more precise radial positioning of the head. Conventionally, head positioning is accomplished by operating an actuator arm with a large-scale actuation motor, such as a voice coil motor, to radially position a head over a selected track on a disc. The large-scale motor lacks sufficient resolution to effectively accommodate high track density discs. Thus, a high resolution head positioning mechanism, or microactuator, is necessary to accommodate the more densely spaced tracks.
Various microactuator designs have been considered to accomplish high resolution head positioning. One such microactuator is a magnetic microactuator assembled from various components and bonded to a suspension gimbal and head interconnect. The components include a bottom keeper, two magnets, a coil separated from the magnets by an air gap, and a top keeper. Once assembled, the components form a vertically disposed magnetic circuit. The magnetic circuit makes use of two distinct materials, a magnetically hard magnet material, and a magnetically soft keeper.
In previous magnetic microactuators, the hard magnet material was divided into two discrete components. These included an upwardly polarized magnet with a north pole adjacent the air gap, and a downwardly polarized magnet with a south pole adjacent the air gap. These magnets are easy to polarize by placing the magnets in a strong and uniform magnetic field. However, it is difficult to assemble the two small magnets because the magnets tend to stick to each other due to their strong magnetic attraction.
The magnetically soft keeper material is necessary to reduce field leakage in the magnetic circuit. Specifically, there is often field leakage around the edges of a bottom keeper located between magnets and disc surfaces which may de-stabilize the recorded bits on the disc. A further problem of the keepers is that the magnetically soft keeper material typically used in magnetic microactuators is not resistant to corrosion. Therefore, keepers are typically nickel plated or otherwise passivated, which not only increases their cost, but also poses manufacturing problems, especially when the coil is fabricated on the top keeper.
Therefore, there is a need in the art for a microactuator design having simplified assembly, reduced field leakage, and improved passivation methods.
The present invention relates to an improved magnetic microactuator with a single magnet, reduced field leakage, and improved passivation methods. The single magnet is polarized on a special fixture into two magnetic regions. There is a transition zone between the two regions with weak magnetization. By making the transition zone as small as possible, the single magnet design is made functionally similar to the prior art dual magnet design. The magnet is made of a suitable alloy which allows for magnetization within a desired temperature and current range.
To reduce field leakage from the magnetic circuit, the bottom keeper is expanded to address the problem of field leakage around the edges of the bottom keeper. The thickness of the expanded region may vary widely while still performing the desired shielding function. A preferred thickness surrounding the magnet is about twice the thickness beneath the magnet. The magnetic microactuator further does not have a top keeper. To make the keeper material more resistant to corrosion, corrosion-resistant alloys with acceptable magnetic properties are substituted for prior art keeper material.